Friend Leukemia virus (FLV) and Moloney murine leukemia virus (MoMuLV) are leukemogenic retroviruses with similar structure and life cycles to several human retroviruses including HIV. FLV is a retrovirus complex which first causes either anemia or polycythemia, depending on the virus strain, and then an aggressive and rapidly fatal erythroleukemia. In addition, this virus can cause myelomonocytic leukemias and T-cell lymphomas. MoMuLV attacks exclusively cells of the lymphoid lineage. A key element of both viruses is the env protein, required for cell infection and viral propagation. This proposal is designed to investigate whether intact animals can be genetically engineered so as to be resistant to viral infection and attendant leukemia. Our first strategy involves use of antisense genes for the env protein. Here, antisense FLV and MoMuLV env constructs driven by promoter/enhancer elements designed to optimize expression in susceptible cells will be introduced. Expression of these genes, the ability of their antisense RNAs to interrupt retroviral gene expression after viral challenge, and the physiologic resistance of the transgenic mice will be assessed. Our second strategy, which normal env gene driven to express in susceptible cells. In this case, we will determine if endogenous, constitutive production of env, which is expected to be exported to the receptor on the cell surface, can block viral infection and render animals immune to MoMuLV-induced disease. A related experiment with transgenic animals, to be conducted with Dr. Palese, is to test the efficiency of ribozymes as antisense vectors. Fragments of influenza DNA that can participate in the ribozyme reaction will be introduced into separate lines of mice, but directed to express in the same tissues by use of the same promoter. Then the transgenic animals will be crossed, and the presence of ribozyme cleavage products assessed in the appropriate tissues of the double transgenics. These latter experiments should help determine if this system of catalytic RNA cleavage can be exploited to extinguish gene translation in vivo.